Noncatalytic halogenation of certain alkylated acrylonitriles



materials.

Patented Apr. 5, 1949 UNITED STATES PATENT OFFICE NONCATALYTICHALOGENATION OF CER- TMN ALKYLATED ACRYLONITRILES of Delaware NoDrawing. Application June 28, 1946, Serial No. 680,082

7 Claims.

This invention relates to a process for eflfecting the halogenation, viasubstitution, of unsaturated organic nitriles.

More particularly, the process is directed to substitutive halogenationin the allyl position of unsaturated organic nitriles containing atleast four carbon atoms and having an olefinic bond between two carbonatoms at least one of which is adjacent to a carbon atom having asubstitutable hydrogen atom attached thereto. The process is carried outin its more general aspects by submitting the above and hereinafterdefined class of unsaturated organic nitriles to the action of ahalogen-at an elevated temperature which promotes substitutive reactionbetween the nitrile and the halogen but below a temperature at whichsubstantial degradation of the unsaturated organic nitrile or thehalogen-substituted unsaturated organic nitrile may occur.

The halogen-substituted unsaturated organic nitriles that are obtainedin accordance with the process of the present invention contain thehalogen atom in the allyl position relative to theolefinic bond, thatis, attached to a non-olefinic carbon atom that is directly linked to anolefinically bonded carbon atom. They are of high value as intermediatesfor the. production of numerous chemical compounds and materials derivedtherefrom, such as pharmaceutical com- ,pounds, special solvents,products serving useful purposes in. the art of synthetic resins, andother Because of the presence in the same molecule of the reactivecarbonitrile group, an olefinic bond, and a reactive halogen atomattached to a carbon atom adjacent to an olefinic carbon atom, thehalogen substituted unsaturated organic nitriles that are obtained bythe practice of the present process are of particular value for thepreparation of a wide variety of useful chemical compounds. The presentinvention provides a process whereby a variety of valuable organiccompounds may be synthesized on a commercial scale at acost'commensurate with industrial requirements, and in good yield andquality.

The unsaturated organic nitriles which may be subjected successfullytosubstitut'rve halogenation in accordance with the process of thepresent invention are those unsaturated organic nitriles which containat least four carbon atoms and at least one olefinic bond between a pairof carbonatoms at least one of which is. directly linked to a. carbonatom of aliphatic nature having a substitutable hydrogen atomattached'thereto, The present invention thus includes Within its scopeonly those unsaturated organic nitriles which containa substitutablehydrogen atom in the allyl position in respect to an olefinic bond. Theun-. saturated organic nitriles that may be halogen substituted inaccordance with the process of the present invention may contain anolefinic bond either in a position conjugate to the polyvalent. bond. ofthe carbonitrile group or in a position non-conjugate thereto. Theolefinic bond thus may be either in the alpha-beta position in respectto the carbonitrile group or it may be elsewhere in the molecule. Ineither case, however, it is essential for the purposes of the presentinvention that the organic nitrile have a substitutable hydrogen atomattached to at least one nonolefinic carbon atom adjacent to anolefinically bonded carbon atom.

Representative unsaturated organic nitriles containing at least fourcarbon atoms and having an olefinic bond in a position conjugate to thepolyvalent bond of the carbonitrile group are, for example, thesecondary, straight chain nitriles such as crotononitrile,2-pentenenitrile, Z-hexenenitrile, Z-heptenenitrile and homologouscompounds and the like. Instead of such straight chain nitriles, theremay be employed analogous branched chain nitriles having an olefinicbond in a position conjugate to the polyvalent bond of the carbonitrilegroup; for example, the unsatu-.

rated nitriles having a substitutable hydrogen in which one R representsan alkyl group and the second R represents a member of the groupconsisting of the hydrogen atom and the alkyl groups, and further tocontain an atom of hy-' drogen in the allyl position relative tothe-alpha,- beta-olefinic bond and to contain a total of not over ninecarbon atoms. Unsaturated organic nitriles that contain the olefinicbond in a posi-:

tion non-conjugate to the polyvalent bond of the carbonitrile group andwhich may be halogen substituted advantageously in accordance with thepresent invention, are for example the straight chain or the branchedchain unsaturated nitriles such as 3-butenenitrile (vinylacetonitrile),3 pentenenitrile, 4 pentenenitrile, 2- methyl-3-pentenenitrile, 3-methyl3 pentenenitrile, 2-isoamyl 4 meth l 3 pentenenitrile, similar alkylsubstituted hexenes having the olefinic bond in a position non-conjugateto the polyvalent bond of carbonitrile group, and analogous substitutedheptenes, octenes, etc. It is preferred to employ in the process of thepresent invention the unsaturated organic nitriles having an olefin bondin a position conjugate to the polyvalent bond of the carbonitrilegroup. The process of the present invention also includes within itsscope the halogen-substitution of unsaturated cyclo-organic nitrileswhich contain an olefinic bond either conjugate or non-conjugate to thepolyvalent bond of the carbonitrile group, such as, for example,2-cyclohexene-1- carbom'trile, 3 cyclohexene 1 carbonitrile, 2-methyl-3-cyclohexene-l-carbonitrile and similar or homologouscyclo-organic nitriles containing a cyclo-olefinic structure. Thesubstituted halogenation of either straight-chain, branched chain, orcyclic olefinic organic nitriles containing more than one olefinic bondalso is contemplated as within the broader aspects of the presentinvention. Representative di olefinic nitriles thus are2,5-hexadienenitrile, 1,3-cyclohexadiene-l-carbonitrile, 4-methyl3,5-hexadiene-nitrile, etc. It will be understood that the foregoing andother compounds falling within the general and/or more limited classesof unsaturated nitriles adaptable to the purposes of the presentinvention, may contain additional substituent groups that are stableunder the conditions of reaction and that do not prevent the desiredhalogen substitution reaction from taking place. Thus, there may beemployed, unsaturated olefinic nitriles containing for example, anaromatic nucleus such as a benzyl group, a phenyl group, and the like, acycloparafiinic group such as the cyclohexyl group, etc., one or morehalogen atoms either different from or the same as the halogen to beintroduced into the molecule, and similar substituent groups.

The process of the present invention is of particular advantage in itsapplication to the alpha, beta unsaturated organic nitriles which havean alkyl substituent group attached to the alpha carbon atom and asubstitutable hydrogen atom on the non-olefinic carbon atom adjacent tothe alpha carbon atom; i. e., to the halogenation via substitution ofmethacrylonitrile and its homologs. This class of compounds may berepresented by the general structural formula \C=CEN R o wherein each Rrepresents either hydrogen or the same or different alkyl radicals. Itappears that the presence of the triply bonded nitrilo nitrogen atom hasa pronounced influence upon the remainder of the molecule in respect toreaction with halogens, although the reasons for such influence are notat all well understood. Thus, whereas tertiary olefins such asisobutylene normally undergo halogen substitution at ordinary andreduced temperatures to the substantial exclusion of halogen additionreactions, introduction of the nitrilo group into, for instance,isobutylene to form methacrylonitrile, alters the reactivity so as tosubstantially obviate halogen substitution under the influence ofordinary or even somewhat elevated temperatures. Thus even attemperatures as high as 200 C. in the case of methacrylonitrile thereaction with chlorine has been found to be without tendency to halogensubstitution. The reaction follows instead, in such a case, the courseof halogen addition to the methacrylonitrile, forming dihalogensaturated nitriles which diifer in essential characteristics from theunsaturated halogen-substituted nitriles obtainable by the process ofthe present invention. The process of the present invention makespossible for the first time the direct substitutive halogenation ofmethacrylonitrile and its homologs, and thereby renders production oftheir halogenation products highly economical and efficient;

The nitriles which may be employed in accordance with the process of thepresent invention may be either in a highly purified form or they may bein admixture with other materials. The product of reaction obtained inthe synthesis of the unsaturated nitriles may be used in the presentprocess without purification if desired. A particularly convenient andeconomical mode of operation involves, for instance, continuouslysynthesizing the desired nitrile as by passing vapors of thecorresponding unsaturated carboxylic acid and ammonia over alumina orother suitable catalyst at an elevated temperature, and then passing theheated reaction product thereby obtained directly into the presentprocess to form the corresponding halogen substituted unsaturatedorganic nitrile.

Although the present process is described broadly with reference to thehalogen and the halogenation, it is of particular value and utility inrespect to chlorination and bromination, via substitution, of the hereindefined class of un saturated organic nitriles. In its preferredembodiment, the process therefore advantageously uses chlorine orbromine as the halogen, and accordingly, results in the preparation ofthe corresponding chlorinated or brominated unsaturated organicnitriles. The use of chlorine as the. halogen is of particular value andits use as the halogen generally is most highly preferred.

In practicing the process of the present invention, the unsaturatedorganic nitrile and the halogen are brought into reactive contact at anelevated temperature that favors halogen substitution reaction betweenthe nitrile and halogen without substantial degradation of the nitrilereactant and/or product, or possible undesired side reactions,decompositions, etc. The exact range of temperature to be employed inany given instance depends to a certain extent upon the other conditionsunder which the reaction is effected, such as time of contact, relativeproportions of reactants, design of apparatus, etc, The optimumtemperature range also differs somewhat with the various nitriles aswell as with the different halogens. In each case, however, there hasbeen found to be a minimum temperature favoring substantial halogensubstitution of the unsaturated nitrile, and the present process iscarried out at a temperature above such minimum temperature. The maximumtemperature used in accordance with the process is determined by themaximum temperature to which the reactants and/or productscan' besubjected under the existing conditions without substantial degradationthereof. Theprocess of the presentinvention is efiected at a temperaturebelow this maximum temperature. stated that the minimumtemperature-desirable is about 250 0., although it will be found that incertain instances either a slightly higher or a slightly lower minimumtemperature will be desirable. It generally is not desirable to employ areaction temperature higher than about 600 the reaction temperaturewithin the range of from about 350 C. to about 550 C.

The reactants may be introduced into the reaction zone either previouslymixed or separately. A particularly convenient procedure involves Jpassing a stream of the unsaturated organic nitrile through an elongatedreaction zone such as a suitable reaction tube, in admixturewith theselected halogen inthe vapor state. The nitrile may be either in theliquid state, if the reaction temperature is below its boiling point atordinary pressures, or it may be in the vapor state. Because of thepossibility that excessive undesiredside reactions between the halogenand the unsaturated nitrile such as halogen addition may occur if thereactants are allowed to remain in admixture for any substantial time ata temper,- ature much below the present reaction temperature, itgenerally is highly desirable to minimize or to entirely eliminate uchprior contact at lower temperatures. This may be accomplished, forinstance by preheating the unsaturated nitrile to-a suitably elevatedtemperature prior to ad'-,

mixture with the halogen and rapidly introducing into the heated'nitrilea stream of gaseous halogen which may be either at normal temperaturesor also may have been preheated to an elevated temperature, and thenimmediately passing the admixed reactants through the reaction zone.

It is not always absolutely necessary, however, to resort to preheatingof the reactants. In certain cases it is satisfactory to minimize theprior, low temperature contact time as by mixing the two reactants inthe cold and then rapidly raising the temperature of the mixture towithin the desired temperature range. When there is employed preheatingof the reactants, it generally is desirable to preheat to within thetemperature range utilized for reaction.

The velocity at which, in the case of continuous operation, the mixedreactants are intermixed and passed through the reaction zoneiscorrelated with the reaction temperature, and alsois dependent in partupon factors such as design of apparatus, extent of preheating, etc. Atany given reaction temperature the reactionmixture .is maintained withinthe reaction zone and at the reaction temperature for a period of timeWhich favors halogen substitution of the nitrile. without substantialdegradation thereof.

In general, it is desirable with any given apparatus to employ themaximum rate of flow con-v sistent with suitable yields, and hence theminimum time practicable during which the reactants are at the reactiontemperature. The halogenationof unsaturated organic nitriles'is an exo--thermic reaction. which may; under. substantially In general, it maybeadiabatic conditions promote flaming or explosion Such possibleflaming.

of the reaction mixture. or explosion may be obviated, for example, byintroducing the gaseous halogen into the stream of nitrile at a velocityexceeding that of flame propagation under the existing conditions. A1-ternatively, the reaction zone may be cooled if desired by suitablemeans apparent to the art, or a diluent may be included with thereactants to reduce their concentration and hence to minimize danger offlaming or explosion. It also is possible to reduce the volumeconcentration of thereactants by carrying out the process under reducedpressure, this being particularly suitable in the event it is desired toemploy vapor phase reactionwith nitriles normally liquid at thereaction,

temperature but which may be volatilized under suitably reducedpressures. If the design of the apparatus is such that excessive heatloss would; 5 occur, thereby cooling the reaction zone to below,

reaction temperature, external or internal heating means may beprovided.

The high temperature substitutive halogenationof unsaturated, organicnitriles may in general be effected with either the halogen or the,

' nitrilepresent in a molar excess. It generally is desired however, toemploy a molar excess of the nitrile over the halogen in the processbecause of the higher yields based on the halogen that thereby areobtained and because of the greater. ease with which the reaction may becontrolled Preferably'the reactants are. employed in a molar ratio ofhalogento nitrile of from about 1:1 to1:5.

In continuous operation of the present proc ess, the reactants inadmixture may be passed through an elongated reaction zone such as may.be provided by a suitably heated or cooled tube,

The tube may be constructed of any suitable thervmallyresistant metalalloy, such as iron, ordinary s'teels, Monel metal, stainless steels,etc. or of other materials such as carbon, quartz, glass,

porcelain, etc. The process may be effected with theireactants in eitherthe liquid phase or the vapor. phase. Vapor phase reaction frequently isadvantageous because of the more complete mix-.- ing'of the reactantsthat is possible. However, in the case for example, of halogenation ofthe higher, less volatile nitriles it frequently is impracticable toemploy vapor phase reaction. Ef-

fecting the reaction in the liquid phase in such cases therefore isparticularly suitable.

The outcome of the process of the present invention is not dependentupon the use or presence of added catalytic materials in the reactionzone, 1 although their presence is not excluded from the broader aspectsof the invention. The presence, in the reaction zone of an added solidmaterial tends; in general to increase the deposition of carbon duringthe reaction and hence generally is to.

be avoided. Because of the increased economy and simplicity of operationthat result, the. pro.c-, ess. in its; preferred embodiments is effectedin for. promptly stopping the reaction. The reaction mixture thus may becooled and the halogen substituted unsaturated nitrile recoveredsubstantially as soon as the reaction mixture exits from the reactionzone, Separation of. the halogen-sub stituted unsaturated nitrile may beeffected, for.

example, by appropriate use of selective. solvents,

by fractional distillation, or by other suitable means. Hydrogenchloride in the reacted mixture may be removed by contacting the mixturewith water, which selectively dissolves the hydrogen chloride.Neutralization of the reaction mixture with a suitable base may beemployed if desired. Any excess of the initial unsaturated organicnitrile may be recycled through the halogenation process if desired.

The following examples will serve to illustrate certain specificembodiments of the present invention:

Example I Methacrylonitrile was volatilized and a stream of the vaporwas heated to a temperature of about 350 C. A stream of chlorine gaspreheated to approximately the same temperature was introduced into themethacrylonitrile vapor in a molar ratio of about 1 mole chlorine to 3.1moles methacrylonitrile. The stream of mixed reactants immediatelythereafter was passed at a rate of .252 total moles reactants per minutethrough a quartz reaction tube having an inside diameter of 2.0 cm. anda length of 50.4 cm. with a thermocouple 0.4 cm. in diameter extendinglengthwise therein. The reactor tube was surrounded by an electricfurnace maintained within the temperature range of 580 C. to 595 C. Themaximum temperature of the reaction mixture as determined by measurementwith the thermocouple was from about 520 C. to 565 C., varying withinthis range during the course of the experiment.

The reacted mixture was passed directly from the exit of the reactortube through a cooling means and then contacted with water to separatehydrogen chloride. The organic phase of the binary mixture thus obtainedwas separated and fractionally distilled.

After removal of unreacted methacrylonitrile the product was found tocontain 66 weight per cent alpha-(chloromethyl) acrylonitrile, and 28.5weight per cent of high boiling material and residue. The product wasfound to contain less than 8 weight per cent of chlorobutyronitriles(betachloroisobutyronitrile and alpha, beta-dichloroisobutyronitrile)and beta-chloro-alpha-methylacrylonitrile. On the basis of chlorineapplied (96% reacted) a yield of Z-(chloromethyl) acrylonitrile of 61%was obtained.

Example II uct was found to contain 65.5% alpha-(chloro-,

methyl) acrylonitrile produced in a 54% yield based upon themethacrylonitrile consumed.

Example III Example IV In order to determine the applicability of thepresent process to the substitutive halogenation of an unsaturatednitrile containing less than four carbon atoms, acrylonitrile wasvolatilized and passed in admixture with gaseous chlorine, at a molarratio of acrylonitrile to chlorine of 3.8:1 and a flow rate of 0.06total mole reactant per minute, through an unpacked quartz tube havingan inside diameter of two centimeters and maintained at 520 C. Littlereaction was evident. At temperatures of 560-570 0., decomposition wasso extensive that carbon deposition plugged the tube in a few minutes.

Example V Example I was repeated employing bromine in place of thechlorine. Alpha-(bromomethyl) acrylonitrile was produced in good yield.

Example VI Alpha-beta-dimethylacrylonitrile was volatilized and passedwith chlorine, at a molar ratio of nitrile to chlorine of 3.7:1 througha quartz reaction tube maintained within the temperature range of 325 to487 C. The reaction mixture leaving the reaction tube was cooled rapidlyand washed by contacting with dilute aqueous sodium hydroxide. Thewashed organic phase was fractionally distilled under reduced pressureto provide ch1or-alpha,betadimethylacrylonitrile in good yield based onthe alpha,beta-dimethylacrylonitrile consumed.

In place of the unsaturated organic nitriles utilized in the foregoingexamples, there may be employed, for instance, other unsaturated organicnitriles having an olefinic bond in the alpha,beta positions and atleast one substitutable hydrogen atom in the allyl position in respectto the olefinic bond. Likewise, there may be employed non-conjugateunsaturated organic nitriles having a substitutable allyl hydrogen atom,as more fully set forth hereinbefore. By means of the process of whichthe foregoing examples provide certain illustrative embodiments halogensubstitution, preferably chlorine or bromine substitution, may beadvantageously effected with the consequent formation of valuable anduseful products.

We claim as our invention:

1. A process for the preparation of chloro-,alpha,beta-dimethyl-acrylonitrile which consists in chlorinatingnon-catalytically alpha,betadimethylacrylonitrile by reactingalpha,beta-di-' methylacrylonitrile in the vapor state with gaseouschlorine in the absence of catalysts at a temperature above about 250 C.but below about 600 C.

2. A process for the preparation of gammachlorocrotononitrile whichconsists in chlorinating non-catalytically crotoncnitrile by reactingcrotononitrile in the vapor state with gaseous chlorine in the absenceof catalysts at a temperature abov about 250 C. but below about 600 C.

3. A continuous non-catalytic process for the preparation of alpha-(chloromethyl) acrylonitrile which comprises mixing a stream of gaseouschlorine with a gaseous stream of methacrylonitrile in a molar ratio ofchlorine to methacrylonitrile between about 1:1 and about 1:5,immediately thereafter passing the stream of reactants through areaction zone maintained at a temperature between about 250 C. and about600 C. and devoid of substances having catalytic activity for thereaction, for a period of time which favors chlorine substitution of themethacrylonitrile Without substantial degradation thereof, andrecovering alpha-(chloromethyl) acrylonitrile from the products issuingfrom the reaction zone.

4. A process for the preparation of alpha- (chloromethyl)acrylonitrilewhich consists in chlorinating non-catalytically methacrylonitrile byreacting methacrylonitrile in the vapor state with gaseous chlorine inthe absence of catalysts at a temperature above about 250 C. but belowabout 600 C.

5. A continuous non-catalytic process for the preparation of analpha,beta-olefinic nitrile substituted in the allyl position relativeto the olefinic bond by an atom of a halogen selected from the groupconsisting of bromine and chlorine which comprises mixing in the vaporphase a halogen selected from the group consisting of bromine andchlorine with an alpha,beta-olefinic nitrile containing at least fourcarbon atoms and of the general formula in which one R represents analkyl group and the second R represents a member of the group consistingof the hydrogen atom and the alkyl groups, said nitrile reactant havingan atom of hydrogen in the allyl position relative to thealpha,beta-olefinic bond and containing a total of not over nine carbonatoms, in a molar ratio of halogen to nitril between about 1:1 and about1:5, immediately thereafter passing a stream of the mixture through areaction zone devoid of substances having catalytic activity andmaintained at a temperature between about 250 C. and about 600 C., andrecovering from the products leaving the reaction zone analpha,betaolefinic nitrile substituted in the allyl position relative tothe apha,beta-olefinic bond by an atom of the halogen reactant.

6. A process for the preparation of an alpha, beta-olefinic nitrilesubstituted in the allyl position relative to the olefinic bond by anatom of chlorine which consists in chlorinating noncatalytically analpha-alkyl-alpha,beta-olefinic nitrile containing at least four carbonatoms and of the general formula in which the R directly attached to thealpha carbon atom relative to the nitrillo group represents an alkylgroup and the second R represents a member of the group consisting ofthe hydrogen atom and the alkyl groups, said nitrile reactant having ahydrogen atom directly linked to the saturated carbon atom adjacent tothe alpha carbon atom and containing a total of not over nine carbonatoms, by reaction in the vapor phase with gaseous chlorine at atemperature between about 250 C. and about 600 C.

7. A process for the preparation of an alpha, beta-olefinic nitrilesubstituted in the allyl position relative to the olefinic bond by anatom oi a halogen selected from the group consisting of bromine andchlorine, which consists in halogenating non-catalytically analpha,beta-olefinic nitrile containing at least four carbon atoms and ofthe general formula n-cikc-os-N in which one B. represents an alkylgroup and the second R represents a member of the group consisting ofthe hydrogen atom and the alkyl groups, said nitrile reactant having anatom of hydrogen in the allyl position relative to thealpha,betaolefinic bond and containing a total of not over nine carbonatoms, by reaction with a gaseous halogen selected from the groupconsisting of bromine and chlorine at a temperature between about 250 C.and about 600 C.

file of this patent:

UNITED STATES PATENTS Number Name Date 2,231,363 Long Feb. 11, 19412,283,237 Spence et a1 May 19, 1942 OTHER REFERENCES Lespieau: Bull.Soc. Chim. de France (3), vol. 33, pp. -67 (1905).

Certificate of Correction Patent No. 2,466,641. April 5, 194-9.

GEORGE W. HEARNE ET AL. I

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows:

Column 3, line 62, for that portion of the formula reading C=CEN read0==O-0= =N;

and that the said Letter Patents should be read with this correctiontherein that the same may conform to the record of the case in thePatent Ofiice.

Signed and sealed this 11th day of October, A. D. 1949.

THOMAS F. MURPHY,

Am'atant Oommimoner of Potash.

